In the experiment on pea breeding,
Mendel observed the different kinds of seeds obtained by crosses from
plants with round yellow seeds and plants with wrinkled green seeds.
Possible types of progeny were:
``round yellow'', ``wrinkled yellow'', ``round green'', and
``wrinkled green.''
And Mendel's theory predicted the associated probabilities of
occurrence as follows.

Round yellow

Wrinkled yellow

Round green

Wrinkled green

Probabilities

9/16

3/16

3/16

1/16

We want to test whether the data from observation
is consistent with his theory--goodness of fit test,
in which the statement of null hypothesis becomes ``the model is valid.''